I just finished reassembling the powervalve on a 99 YZ250. Initially, I disassembled it to replace the shaft seal located on the right hand/throttle side of the cylinder. (This is the seal that seals the powervalve assemblychamber from the governor actuator chamber.) But once I got the valve completely taken apart, I discovered the centervalve flange to be broken off, which was enabling the valve to protrude a few extra mm into the cylinder and make slight contact with the piston. (This explained a compressed ring landing on the piston.) We obtained a new powervalve, shaved it to accomodate the big bore (265 cc) and reassembled. Everything went together fine but I did notice one thing that bothered me. The hole that the powervalve shaft rides in (immediately adjacent to the seal I replaced) is severely wollered out. The shaft has obviously been walking around a bit. I'm hoping this was occuring because of the broken centervalve and that the new centervalve will resolve. Any comments on this would be greatly appreciated. Bench testing of the powervalve assembly looked good; and short of replacing the cylinder, I don't know what could be done to fix this anyway; so I reluctantly reassembled. The motor sounds good, really good. But is this a time bomb? Thanks in advance and sorry for the ramble. Just want to make sure I paint the complete picture.